This invention relates to internal combustion engine analyzers, and more particularly to a distributorless ignition interface for interfacing existing engine analyzers with distributorless ignition systems.
Until recently, ignition systems for internal combustion engines incorporated a distributor. However, the use of distributorless ignition systems is becoming more and more prevalent. Distributor type ignition systems consist of a single coil and a distributor to distribute sparks to individual spark plugs. Such systems provide only one firing per cylinder per engine cycle and all firings are of the same polarity. In contrast, waste spark distributorless ignition systems do not have a distributor and have one coil for every two cylinders, which are conventionally referred to as companion cylinders. Spark firings occur every engine revolution, or twice per engine cycle, with the spark plugs for companion cylinders firing at the same time from the same coil. This results in a compression firing and an exhaust firing for every cylinder for each engine cycle. The polarity in one cylinder is in the positive direction and the polarity in the companion cylinder is in the negative direction.
With a distributorless ignition system, there is no common point from which secondary or high voltage waveform signals for all cylinders can be coupled to an engine analyzer for analysis. In addition, there is no common primary circuit from which a primary or low voltage signal can be detected for all cylinders. Also, instead of one firing for each cylinder, there are two firings for each cylinder which occur 360.degree. apart on crank rotation, one cylinder firing in the compression cycle and one cylinder firing in the exhaust cycle. Because of these distinctions, it is not possible to use engine analyzers designed for analyzing internal combustion engines having conventional distributor type ignition systems in analyzing the operation of internal combustion engines having distributorless ignition systems without adapting the existing engine analyzer to respond to a distributorless ignition systems.
Conventionally, internal combustion engines employing a distributorless ignition system have an electronic control module which is located in the passenger compartment or under the hood. The control module controls sequential energization of a set of coils located in a housing, commonly referred to as a coil pack, and mounted in close proximity to the engine. A wiring harness and associated connectors interconnect the electronic control module to the coil pack to extend energizing signals to the coils in sequence for firing spark plugs connected in series with the coil secondary windings. This connection is made at the coil pack. However, it is often very difficult to gain access to the coil pack. In some cars, the coil pack is underneath the engine, for example.
Distributorless ignition adapters have been proposed. However, most of the known adapters require disconnection of the electronic control module from the coil pack and connection of the distributorless ignition adaptor between the coil pack and the electronic control module. These adapters must be connected in circuit with the control modules because the adapters derive operating signals from the control module. Connection of the adaptor in circuit with the control module on the car is a very time consuming and difficult process. It may take forty-five minutes to connect the adapter in circuit with the control module.
One known distributorless ignition adaptor does not require connection to the control module and thus obviates the need for disconnecting the electronic control module from the coil pack. However, in use of this adaptor, it is critical how the probes are connected to the engine. If the probes are not connected to the proper spark plugs, the adaptor will not work. Also, information indicative of the type of engine under analysis must be entered into the unit. Moreover, the test lead harness includes a terminal block and six test leads which are permanently connected thereto. Thus, if a test lead becomes damaged, the entire harness must be replaced.
Known distributorless ignition adapters are characterized by the common shortcoming that they can only be used in testing certain engines.